The `runZoned` method deprecates the `onError` parameter.
Invocations using that parameter must use `runZonedGuarded` instead.

This prepares Flutter for the deprecation. The same places need to be migrated to using
`runZonedGuarded` when the SDK change has been ported to Flutter.
Then the deprecated member will be removed in a follow-up CL when the most important
packages have been migrated.